Rhodium-Catalyzed Hydroformylation of 1-Hexene in an Ionic Liquid: A Molecular Dynamics Study of the Hexene/[BMI][PF6] Interface.

We report a mol. dynamics study of biphasic systems involved in the rhodium-catalyzed hydroformylation of 1-hexene in the 1-butyl-3-methyl-imidazolium hexafluorophosphate ionic liq. ([BMI][PF6] IL). We first describe the neat [BMI][PF6] interfaces with hexene (the substrate) and heptanal (the linear reaction product) as org. phases. The former interface is molecularly sharp with BMI+ cations preferentially oriented "perpendicular" (i.e., pointing their Bu chains toward the org. phase), whereas hexene mols. tend to be somewhat parallel to the interface. The interface with heptanal is approx. twice as broad, due to BMI+···O(heptanal) attractions, and the solvent mols. are disordered at the interface. No IL ions solubilize in the org. phase(s) whereas ca. 2-3 hexene or heptanal mols. diffused into the IL phase. The presence of the CO and H2 gases does not modify the nature of the hexene/IL interface, as these gases are mainly solubilized in the org. phase, resp., as dild. species and in the form of a "gaseous" droplet. In the IL phase, one finds a few CO monomers, whereas the less sol. H2 mols. spend only transient excursions. We next simulate the phase sepn. of "randomly mixed" IL/hexene liqs. with the [RhH(CO)L3] precatalyst as a solute, comparing the PPh3 to the TPPTS3- ligands (L). The phases sep. much more slowly than in the case of classical liqs., and the neutral complex with PPh3 ligands solubilizes in the hexene phase, displaying loose dynamical contacts with the IL interface. This contrasts with the -9 charged [RhH(CO)(TPPTS)3]9- complex that sits "immobilized" on the IL side of the interface and is mainly solvated by BMI+ cations. Finally, we characterize the solvation of -6 charged [RhH(CO)(TPPTS)2]6-, [RhH(CO)2(TPPTS)2]6-, and [RhH(CO)(TPPTS)2(hexene)]6- complexes involved as reaction intermediates in the hydroformylation reaction and of the free TPPTS3- ligand itself in the bulk IL. [on SciFinder(R)]

Références

Titre
Rhodium-Catalyzed Hydroformylation of 1-Hexene in an Ionic Liquid: A Molecular Dynamics Study of the Hexene/[BMI][PF6] Interface.
Type de publication
Article de revue
Année de publication
2007
Revue
J. Phys. Chem. B
Volume
111
Pagination
4951–4962
ISSN
1520-6106
Soumis le 12 avril 2018